At one time there was a live-and-let-live attitude among social scientists. Economists were almost exclusively concerned with behavior directly involved in the production and consumption of market goods and services. Non-market activities ranging from war to politics to marriage were considered the province of political science, sociology, anthropology, or psychology. However, in the last forty years, economists have made a determined effort to expand the reach of their discipline into areas of human behavior that were once considered off limits. It is not clear what motivated this expansionist urge. It would be nice to say that having settled all the questions in their own field, economists went looking for new frontiers to conquer. This is not the case.